Multi-shelved convection microwave oven

ABSTRACT

An oven, is provided that includes multiple heat transfer means, including convection and microwave heat transfer means. The oven includes a cooking chamber, a blower and at least a shelf disposed within the cooking chamber. The shelf is designed to act as a food support as well as a conduit through which heated air passes into the cooking chamber. The microwave heating means comprises a microwave source and wave guide through which microwaves travel. The wave guide includes a plurality of openings through which microwaves can pass into said cooking chamber. In the preferred embodiment, the openings in the wave guide are positioned to correspond with the predetermined minima or maxima for the microwave wavelength propagating within the wave guide. An electric heating element may also be disposed within the cooking chamber to provide an alternative heating source.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. Provisional Patent Application Ser.No. 60/130,067 filed Apr. 19, 1999, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a multi-shelved oven having multipleheating means, including convection, microwave and radiant food heatingmeans.

BACKGROUND OF THE INVENTION

The oven disclosed herein relates primarily to ovens suitable for use inthe commercial food service industry, such as fast food restaurants, andother food service application where there is great variety in the foodproducts prepared, the need for speedy thermalization of food and spaceconstraints. While various oven designs are known and available forcommercial food service applications, there still exists a need for anefficient and effective oven that allows for simultaneous cooking ofdifferent food products requiring different heat treatments. Singlecavity ovens have been designed heretofore that include microwave andconvection heat transfer cooking means. While such ovens meet the needsof certain commercial food service applications by providing rapidthermalization and cooking, the inability to cook different foodssimultaneously with different heating conditions and cook cycles doesnot provide needed flexibility. Furthermore, known combination ovensoften require mechanical means to stir the microwave or move the foodproduct in order to achieve even microwave heat transfer to the foodproduct.

The present invention provides an oven that meets a need in the foodservice industry for an oven provides rapid heating/cooking and theability to cook multiple food products simultaneously under differentconditions and cook cycles. Moreover, the ovens of the present inventionprovide a microwave heating means that does not require mechanicalstirring of microwaves or movement of food products to achievesubstantially uniform distribution of microwave energy into the cookingcavities of the oven.

SUMMARY OF THE INVENTION

The present invention provides a novel thermal food treatment systemthat combines multiple means of heating in a single system.

In one aspect of the invention an oven is provided that includes acooking chamber, a blower and a shelf disposed within the cookingchamber. The shelf has a unique design in that it has an inlet openingand cavity in fluid communication with the blower and at least oneopening in fluid communication with the cooking chamber through whichtemperature controlled air can flow into the cooking chamber to cookfood by convection heating. In another aspect of the invention, the ovenfurther comprises a microwave heating source for heating food productswithin said cooking chamber, thereby providing multiple heating methods(convection and microwave).

In another aspect of the invention, the microwave heating means includesa microwave source and wave guide through which microwaves travel. Thewave guide includes a plurality of openings through which microwaves canpass into said cooking chamber. In a preferred aspect of the invention,the openings in the wave guide are positioned to correspond with thepredetermined minima or maxima for the microwave wavelength propagatingwithin the wave guide. That is the spacing of the wave guide openingsoccurs at multiples of predetermined minima and/or maxima for themicrowaves within the guide generated by the microwave source, mostcommonly a magnetron.

In another aspect of the invention, a heating element can be mountedwithin the cooking chamber, providing an additional heating means. In apreferred embodiment, a movable, reflective stirrer is positioned abovethe heating element to reflect heat from the heating element toward afood product.

In yet another aspect of the invention the shelf includes a plurality oflouvers protruding from the top surface of the shelf for supporting afood receptacle thereby allowing air to flow freely beneath the foodproduct or receptacle. The louvers have openings that direct temperaturecontrolled air in a direction substantially parallel to the top of theshelf.

In a preferred embodiment of the invention, the cooking chambercomprises a first cooking cavity and a second cooking cavity andincludes a first shelf and a second shelf. The first shelf has an inletopening and cavity in fluid communication with a blower and the secondshelf has an inlet opening and cavity in fluid communication with ablower. Further, both the first and second shelves have at least oneopening in fluid communication with the first cooking cavity and secondshelf having at least one opening in fluid communication with saidsecond cooking cavity, respectively. In a preferred aspect of thisembodiment, microwave heating is provided in the first and secondcavities through wave guides, preferably a pair of wave guidesassociated with each cavity. The preferred wave guide arrangement againprovides a wave guide having a predetermined minima and maxima andopenings in the wave guide positioned to substantially correspond theminima or maxima, thereby providing efficient and even distribution ofmicrowave energy into the cooking cavities along the length of the waveguide.

In yet another aspect of the invention, the blower which suppliestemperature controlled air to the cooking chamber has an exhaust openingin its housing through which a portion of the temperature controlled airis exhausted from the system. In this arrangement, the oven furtherincludes an ambient air intake opening in fluid communication with theblower whereby the blower draws airs through the intake opening toreplace the exhausted air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is front view of the oven (three cavity configuration);

FIG. 2 is a front view of the interior cooking chamber of the oven(three cavity configuration);

FIG. 3 is a front perspective view of the interior cooking chamber andportions of the convection heat transfer and microwave heat transfersystems of the oven (three cavity configuration);

FIG. 4 is a front perspective view of the interior cooking chamber andportions of the convection heat transfer and microwave heat transfersystems of the oven (three cavity configuration);

FIG. 5 is a front perspective view of the interior cooking chamber andportions of the convection heat transfer system of the oven (threecavity configuration), including the food product shelf;

FIG. 6 is a view of the interior cooking chamber depicting the electricheating element within the cooking chamber;

FIG. 7 is a left side view of the oven with the left panel of theexterior cabinet removed to show portions of the convection heatingsystem of the oven (three cavity configuration);

FIG. 8 is a perspective view of the food shelf which serves as a conduitthrough which temperature controlled air into the cooking chamber of theoven;

FIG. 9A is a perspective view of an alternative embodiment of the shelf;

FIG. 9B is a cross section view of the alternative embodiment of theshelf depicted in FIG. 9A;

FIG. 10 is a perspective view of a product support rack;

FIG. 11 is a perspective view of an embodiment of an air delivery ductfor the convection heat transfer system of the oven;

FIG. 12 is a perspective view of a preferred alternative embodiment ofan air delivery duct for the convection heat transfer system of theoven;

FIG. 13A is a front view of a filter assembly for filtering air exitingthe cooking chamber;

FIG. 13B is side view of the filter assembly of FIG. 13A;

FIG. 13C is schematic depiction of the accordion fold filter plate ofthe filter assembly of FIG. 13A;

FIG. 14 is a side view of a bracket for supporting the filter assemblyof FIG. 13A on the side wall of the interior cooking chamber of theoven;

FIG. 15 is schematic depiction of a control system for the oven of thepresent invention (three cavity configuration);

FIG. 16 is a perspective view a two cavity configuration of the oven;

FIG. 17 is a partial perspective view of the interior cooking chamberand microwave heating system for the oven (two cavity configuration);

FIG. 18 is a perspective view of the microwave heating system for theoven (two cavity configuration);

FIG. 19 is a partial perspective view of the cooking chamber and ovenconfiguration with partial exhaust of temperature controlled air stream;

FIG. 20 is a partial perspective view of the ambient air intake andpartition chamber aspects of a preferred embodiment of the two cavityconfiguration of the oven; and

FIG. 21 is a perspective view of the reflective stirrer of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The description of the invention provided below is made with referenceto the drawings attached hereto. The drawings have been consecutivelynumbered as FIGS. 1–23.

In FIG. 1, there is shown one embodiment of the oven 10 of the presentinvention. Oven 10 includes an exterior cabinet 12 defined by exteriorside walls, exterior top and bottom walls and an exterior rear wall.Preferably said walls are constructed of a stainless steel material.Hingedly secured to the front of the oven is door 14 which permits foodproducts to be placed in and out of the interior of the oven. A handle16 with latching means is secured to door 14 to allow the door to besecured in a closed position during cooking. The door 14 is designed byknown conventional means for preventing microwave leakage from thechamber 18 while the door is closed. Referring to FIGS. 2–4, 16–17 and19, chamber 18 is defined by interior side walls 19 and 21, back wall23, top wall 25 and bottom wall 27 (collectively the oven chamberinterior walls). Preferably said oven chamber interior walls areconstructed of a stainless steel material. As depicted in FIGS. 1 and 5(three cavity oven) and FIGS. 16–17 and 19 (two cavity oven), chamber 18further comprises a plurality of cooking cavities 18 a.

Referring to the three-cavity oven of FIGS. 1–5, disposed within thechamber 18 of the oven are upper shelf 20, intermediate shelf 22 andlower shelf 24, preferably constructed of a stainless steel material.Shelves 20 and 22 are movably mounted within the oven chamber 18 and arepositioned atop brackets to hold the shelves in position. Bottom shelf24 can rest on the bottom of the oven chamber or, if desired, can reston a bracket as well. Said brackets are generally shown by referencenumeral 30 and are secured to the interior side walls of the oven cavityon opposite sides of the cavity walls. By providing removable shelvesthey can be more easily cleaned.

Referring to FIGS. 2, 5 and 8, the shelves 20, 22 and 24 shall bedescribed in greater detail. Each shelf is designed to not only supporta food product but is also designed as a conduit through whichtemperature-controlled (e.g. heated) gas (preferably air) passes andprovides convection heating to food products within each oven cavity 18a. As shown in the above referenced figures, each shelf has a topportion 31, a bottom portion 32, side portions 34 and 36, rear portion38 and front portion 40, defining shelf cavity 41. Front portion 40 isdisposed within the chamber of the oven adjacent interior oven chamberside wall 19. Further, the front wall 40 of each shelf has openings 42and 44 through which temperature controlled air can pass into the shelfcavity 41. After the temperature controlled air is disposed into theshelf cavity, the air then passes through openings 52 in louvers 50which project from the top portion 31 of each shelf. The louvers 50 arepositioned at spaced areas and permit air to exit via openings in thelouvers in a direction substantially parallel to the top portion of theshelf, at least as it initially exits a louver 50. The openings onlouvers 50 are best seen in FIGS. 5 and 8 and are represented byreference numeral 52. When temperature controlled gases exit openings 52into the oven cavity, food products disposed within the oven cavity areheated via convective heat transfer. One advantage of the louveredopenings projecting from the shelf is that when a pan or other foodreceptacle is placed on the shelf, heated air travels freely beneath thepan and between the louvers providing very effective convective heattransfer.

In an alternative embodiment of the shelf design, the louvers areinverted and do not project from the top of the shelf, but insteadproject into the shelf cavity. In this configuration the louvers actlike scoops within the shelf cavity. While this configuration does notallow air to flow freely beneath a food tray disposed over the openings,a wire rack 900 (FIG. 10) may be placed on the shelf to lift the foodreceptacle (or food) from the top surface of the shelf, therebyproviding satisfactory convection heat transfer.

In yet another alternative embodiment of the shelf shown in FIGS. 9A and9B, the top surface of the shelf 31 a has vertically extendingprotrusions 50 a, recessed areas or surfaces 46 and openings 48 disposedin the recesses areas. The arrows shown in FIG. 9B generally depict thedirection of air travel into the shelf cavity 41 a and through openings48. Like the louver configuration (noninverted) described above, oneadvantage of the shelf design depicted in FIGS. 9A and 9B is that when apan or other food receptacle is placed on the shelf, heated air travelsfreely beneath the pan and between the louvers providing very effectiveconvective heat transfer.

Temperature controlled air is delivered into each shelf by blowerassemblies 60 (FIG. 4). As shown in FIG. 4, each blower assembly 60comprises a blower housing 64, a blower wheel 66 and a shaft 68 operablyconnected to a motor which rotates each blower wheel. In the preferredembodiment of the invention, each blower wheel is turned by a singleaxle 68 which is operably connected to a motor means. A 1/10 horsepowermotor has been found to be adequate. A blower wheel of the forwardinclined type has also been found to be adequate. Air is drawn into theblower housing and is disposed into tapered ducts 62 which, as shown,are disposed between the cabinet side wall and the oven chamber sidewall 19.

In FIG. 4, specific reference numerals are provided only with respect tothe tapered duct which is in fluid communication with the lower shelf.However, the features of the lower blower and duct assemblies areessentially identical to the middle and upper blower and duct assembliesand therefore descriptions for the latter are not repeated. As shown inFIG. 4, each tapered duct has a proximal end 162 and a distal end 168.An inlet opening is provided at proximal end where temperaturecontrolled gas from blower 60 enters the duct (i.e., inlet opening 164is in fluid communication with the blower assembly associated with theduct). Further, each tapered duct 62 has an elongated opening 70 at thebottom inward facing wall and also has a plurality of orifices 72. Asshown in this embodiment, the orifices 72 and elongated opening 70 areformed in the side wall 19 of the oven chamber 18 (FIG. 12) with theremainder of the duct 62 being formed by two tapered side walls and atop wall. Temperature controlled gases entering each duct 62 exitthrough openings 72 into the respective oven cavities to heat the foodproduct contained within said cavities. Further, as shown, a portion ofthe air entering each duct 62 also exits through opening 70 and flowsrespectively into the shelf cavities 18 a of shelves 20, 22 and 24. Inother words, each tapered duct feeds a separate shelf (20, 22, 24) andalso feeds temperature controlled air through orifices 72 above eachshelf (20, 22, 24). Accordingly, as described above, convective heattransfer is achieved by the present oven design through orifices locatedin the oven cavity side wall above each shelf and also through theshelves themselves through the louvers disposed on the top portion ofeach shelf. In an alternative arrangement, the oven would not includeorifices 72 and therefore all heated gas would flow from ducts 62 intothe shelf associated with the duct.

Referring to FIGS. 4–7, air return openings 90 are provided in side wall19 within each cooking cavity 18 a for the return of gas from eachcooking cavity to blowers 60. By providing air return ports within eachcavity 18 a, each cavity can function as an independent convection oven,thereby allowing cooking of different foods at different temperaturesand on different cycles. In an alternative embodiment of the invention(FIGS. 13A–C and 14), the air return openings 90 may be covered by afilter assembly 300 mounted to side wall 19 by a bracket 302 or otherknown means to prevent food particles, grease and other materials fromescaping the cooking cavity through the return openings. A preferredfilter assembly 300 is shown in FIGS. 13A–C and 14 and comprises afilter frame 304 which supports a perforated metal plate 306 that isfolded in an accordion fashion thereby providing a greater surface areaover which return air passes before exiting the cooking chamber throughthe return openings.

The temperature of the circulated air or gas can be controlled by anyknown means. One suitable means to heat and control the temperature ofthe air is by well known electric heating rods 80 (i.e., Calrod) (FIG.7) or “gas burner” (not shown). Heating rods 80 can be disposed in anysuitable location. In the preferred embodiment, heat rods are placed asshown in FIG. 7 in the return air path for the oven. FIG. 7 shows justone heating rod placed between the upper and middle ducts 62 in the areabetween the exterior cabinet side wall and the cavity side wall 19.Preferably, a heating element is placed above each duct 62 through theopenings 82 shown in FIG. 7.

As it relates to the tapered duct design, duct 62 may have a constanttaper from proximal end 162 to distal end 168 as shown in FIGS. 3–5 and7 or may have multiple degrees of taper as shown by the dashed lines inFIG. 11. As shown in FIG. 11 and denoted by the cross hatched lines,duct 62 may have a dual taper configuration, which has been found toprovide even air flow from the orifices along the length of the duct.More particularly, in the dual taper configuration of duct 62, said ducthas a first horizontal tapered portion 160 adjacent proximal end 162 andinlet opening 164 (i.e., the opening where air from the blower entersthe duct) and a second horizontal tapered portion 166 adjacent thedistal end 168. As shown, the first horizontal tapered portion 160 has agreater angle of taper than the second horizontal tapered portion 166which has a lower slope. Preferably, the first horizontal taperedportion 160 extends approximately one-quarter to one-half of the lengthof the duct. The degree of taper in the first and second horizontaltapered portions may vary. Preferably, the first horizontal taperedportion tapers down 1 inch for every 1 to 3 inches of length and thesecond horizontal tapered portion tapers 1 inch for every 7 to 16 inchesof length. By providing a dual taper, it has been found that the air isdistributed more evenly along the length of the duct from proximal end162 to distal end 168. In a most preferred embodiment of the duct 62shown in FIG. 12, said duct not only includes the dual taperhorizontally along its length described above, but also includes avertically tapered portion 170 adjacent proximal end 162 to furtherenhance air flow into the duct and even distribution of heated air intothe oven chamber along the length of the duct.

After the temperature controlled air enters the oven cavity 18 a throughthe above-described orifices 72 (optionally) and shelves, air isreturned to the blower housing through return openings 90 in the ovencavity side wall 19 (i.e, the cavity wall adjacent each duct 62) (seeFIGS. 2–5). The air returning through openings 90 is heated by heatingelement 80 before entering the blower housing where the heated air isrecirculated into the oven cavity through the ducts 62.

Optionally, an electric heating element 101 (e.g., Calrod heatingelements) may also be disposed adjacent the top of the oven cavity so asto provide a means for broiling food products disposed on the uppershelf (see FIGS. 1, 2 and 6).

The present oven also provides means for heating food product viamicrowave energy. In one embodiment of the invention shown in FIGS. 2and 3, microwaves are disposed into the oven cavity through microwaveopenings 200 formed in the side wall 21 of the oven cavity. Side wall 21is disposed opposite of oven cavity side wall 19. As shown in thepreferred embodiment, there are three series of openings 200, each beingserved by a separate magnetron assembly 210. The type (i.e. power) ofmagnetron used is a matter of choice and is based on well knownselection factors. Use of 2450 MHz magnetrons were found suitable in theembodiment shown in FIGS. 16–18.

In the embodiment shown in FIGS. 2 and 3, each magnetron 210 feedsmicrowaves into and through a conduit 212 associated with the particularmagnetron assembly and through the openings 200 and into the ovencavity. The openings 200 and conduit structure 212 are arranged suchthat a more uniform dispensing of microwave is provided within the ovencavity. A preferred configuration for the openings 200 is shown in thefigures. Other configurations may also be determined and will varyaccording to the design and dimensions of the cooking cavity. As shownin the figures, each cavity 18 a has its own independent microwavesource (i.e., magnetrons assemblies). Thus, heating of food productsdisposed in different cavities can be provided at different rates and ondifferent cycles by separately controlling each magnetron. A schematicrepresentation of the heating controls for the embodiment of FIGS. 1–5is shown in FIG. 15.

In a preferred embodiment of the invention shown in FIGS. 16–20 (twocavity design), microwave energy from magnetrons 410 is fed into eachoven cavity 18 a through a pair of wave guides 400, 402 (i.e., conduits)disposed above each cavity. Thus, each cavity 18 a has its ownindependent microwave source. Each wave guide includes a plurality ofopenings 404, preferably slots, through which the microwaves travel intothe cooking cavity. The slots 404 are spaced to provide substantiallyeven microwave distribution along the length of the wave guide.Specifically, the slots are spaced approximately at multiples of thecalculated minima or maxima for the microwaves generated by themicrowave source, i.e. magnetron. The minima and maxima for a particularwave guide and magnetron are calculated by known means. Microwave maximaand minima for various wave guide designs and microwave frequencies alsocan be readily determined by reference to tables published by magnetronsuppliers, such as Continental Microwave & Tool Co., Inc, Hampton, N.H.As shown, slots 404 are preferably disposed at angles in relation to thelength of wave guides which run generally from the back towards thefront of each cavity. Further, as shown in FIGS. 17–18, blowersassemblies 500 are preferably provided to cool the magnetrons 410 duringoperation.

In a preferred embodiment of the invention reciprocating reflectivestirrers 600 are disposed above the heating elements at the top ofheating chamber 18 for reflecting heat from the heating element towardthe shelf below. Preferably the stirrers are made of a material that isalso microwave reflective so that enhanced stirring of microwaves isachieved, thereby promoting evenness of cooking. A suitable stirrermaterial is stainless steel. As shown, the reflective stirrer 600 isoperably connected to bearing 602 which is moved by link 604, which inturn is connected to a drive link 606 driven by motor 608.

In the embodiment of the invention shown in FIGS. 16–20, it should benoted that chamber 18 comprises two cooking cavities 18 a and that twodoors 700 are used to seal the oven. Another feature of an embodiment ofthe invention provides for the exhausting of a portion of thetemperature controlled cooking air from the blower housing. Referring toFIGS. 17–19, there is shown a exhaust opening 702 in blower housing 64through which a portion of the temperature controlled gas is exhaustedfrom the oven via stack (or conduit) 704. The exhausting of air from thesystem induces ambient air to be drawn through intake opening 706disposed at the back of the oven. Ambient air is then drawn intopartition chamber 708 disposed between the upper and lower cavities 18a. Air from partition chamber 708 is then drawn through openings 710 toboth the upper and lower blower assemblies 60 which are in fluidcommunication with the partition chamber. Exhaust air flow and “make up”ambient air flow into the system is depicted by the arrows in FIGS. 19and 20. The location of the partition chamber between the cookingcavities of the oven is particularly advantageous since the heat fromthe cooking cavities heats the air in the partition chamber, thus actingas a heat exchanger to preheat ambient air.

FIGS. 1 and 16 generally depict the control panel (or controller) 450for the embodiments described herein. Preferably, the controller 450 hasthe capability to control microwave heating power and cook cycle times,and is capable of being programmed for particular food cookingapplications. Likewise, it also is preferable that the controller 450control the convective heat transfer aspects of the invention (e.g.,blowers 60 and heating elements) and the reflective stirrers describedabove.

The present invention is not limited to the examples illustrated above,as it is understood that one ordinarily skilled in the art would be ableto utilize substitutes and equivalents without departing from thepresent invention.

1. An oven comprising: a cooking cavity defined by a door and aplurality of walls; said cooking cavity having a length, width andheight; a first microwave source for producing microwaves; a first waveguide having a length which traverses said length or said width of saidcooking cavity; said first wave guide providing a conduit through whichsaid microwaves travel; said first wave guide having a plurality ofslots intersecting the centerline of its length; said slots spacedappropriately at multiples of the calculated minima or maxima for themicrowaves generated by said microwave source; and through which saidmicrowaves can pass into said cooking cavity.
 2. The oven of claim 1further comprising: a second microwave source and a second wave guidethrough which microwaves travel, said second wave guide having a lengthwhich traverses said length or said width of said cooking cavity; saidsecond wave guide providing a conduit through which microwaves from saidsecond microwave source travel; said second wave guide having aplurality of openings along its length through which said microwaves canpass into said cooking cavity.
 3. The oven of claim 2 further comprisinga blower that circulates heated gas into said cooking cavity.
 4. An ovencomprising: at least one cooking cavity; a blower; a shelf disposedwithin each said cooking cavity and defining the bottom of said cookingcavity, each said shelf having an inlet opening and cavity in fluidcommunication with said blower, each said shelf having at least oneopening in fluid communication with said cooking cavity in which it isdisposed through which temperature controlled gas can flow into saidcooking cavity; at least one air return opening in each said cookingcavity in fluid communication with said blower for return of saidtemperature controlled gas to said blower; and a microwave heatingsource and wave guide through which microwaves travel, said wave guidehaving a plurality of openings through which said microwaves can passinto at lease one cooking cavity, wherein said microwaves traveling insaid wave guide have a wavelength and predetermined minima and maxima,said openings in said wave guide being positioned to substantiallycorrespond with said minima or maxima.
 5. The oven of claim 4 furthercomprising a heating element within at least one cooking cavity.
 6. Theoven of claim 5 further comprising a movable stirrer positioned abovesaid heating element, said stirrer being capable of reflecting heat fromsaid heating element toward said shelf in said cooking cavity.
 7. Theoven of claim 6 wherein said stirrer is constructed of a microwavereflective material.
 8. The oven of claim 4 wherein said shelf has a topsurface and a plurality of louvers protruding from said top surface forsupporting a food receptacle above said top surface.
 9. The oven ofclaim 8 wherein said at least one opening in said shelf is configured toproject said temperature controlled gas in a direction that issubstantially parallel to said top surface of said shelf.
 10. The ovenof claim 4 further comprising a filter adjacent said air return openingfor filtering entrained materials from said temperature controlled gas.11. An oven comprising: a first cooking cavity and a second cookingcavity; a blower; a shelf disposed within each said cooking cavity anddefining the bottom of said cooking cavity, each said shelf having aninlet opening and cavity in fluid communication with said blower, eachsaid shelf having at least one opening in fluid communication with saidcooking cavity in which it is disposed through which temperaturecontrolled gas can flow into said cooking cavity; at least one airreturn opening in each said cooking cavity in fluid communication withsaid blower for return of said temperature controlled gas to saidblower; a first microwave source and a first wave guide through whichmicrowaves travel, said first wave guide having a plurality of openingsthrough which said microwaves can pass into said first cooking cavity;and a second microwave source and a second wave guide through whichmicrowaves travel, said second wave guide having a plurality of openingsthrough which said microwaves can pass into said second cooking cavity,wherein said microwaves traveling in said first wave guide have awavelength and predetermined minima and maxima, said openings in saidfirst wave guide being positioned to substantially correspond with saidminima or maxima; and wherein said microwaves traveling in said secondwave guide have a wavelength and predetermined minima and maxima, saidopenings in said second wave guide being positioned to substantiallycorrespond with said minima or maxima.
 12. The oven of claim 11 whereinsaid blower comprises a blower housing having an exhaust opening throughwhich a portion of said temperature controlled air is exhausted fromsaid blower housing, said oven further comprising an ambient air intakeopening in fluid communication with a chamber disposed between saidfirst and second cooking cavities, said chamber being in fluidcommunication with said blower wherein said blower draws air from saidchamber.
 13. An oven comprising: a first cooking cavity and a secondcooking cavity; a blower; a shelf disposed within each cooking cavityand defining the bottom of said cooking cavity, each said shelf havingan inlet opening and cavity in fluid communication with said blower,each said shelf having at least one opening in fluid communication withsaid cooking cavity in which it is disposed through which temperaturecontrolled gas can flow into said cooking cavity; at least one airreturn opening in each said cooking cavity in fluid communication withsaid blower for return of said temperature controlled gas to saidblower; a first microwave source and a first wave guide through whichmicrowaves travel, said first wave guide having a plurality of openingsthrough which said microwaves can pass into said first cooking cavity; asecond microwave source and a second wave guide through which microwavestravel, said second wave guide having a plurality of openings throughwhich said microwaves can pass into said second cooking cavity; a thirdmicrowave source and a third wave guide through which microwaves travel,said third wave guide having a plurality of openings through which saidmicrowaves can pass into said first cooking cavity; and a fourthmicrowave source and a fourth wave guide through which microwavestravel, said fourth wave guide having a plurality of openings throughwhich said microwaves can pass into said second cooking cavity, whereinsaid microwaves traveling in said first wave guide have a wavelength andpredetermined minima and maxima, said openings in said first wave guidebeing positioned to substantially correspond with said minima or maxima;wherein said microwaves traveling in said second wave guide have awavelength and predetermined minima and maxima, said openings in saidsecond wave guide being positioned to substantially correspond with saidminima or maxima; wherein said microwaves traveling in said third waveguide have a wavelength and predetermined minima and maxima, saidopenings in said third wave guide being positioned to substantiallycorrespond with said minima or maxima; and wherein said microwavestraveling in said fourth wave guide have a wavelength and predeterminedminima and maxima, said openings in said fourth wave guide beingpositioned to substantially correspond with said minima or maxima.
 14. Athermal treatment apparatus comprising: at least one thermal treatmentcavity; a blower in fluid communication with each said cavity forcirculating temperature controlled gas in said at least one cavity; ashelf disposed within said at least one thermal treatment cavity, saidshelf comprising (a) a top portion having an upwardly facing topsurface; said top portion having a plurality of openings through whichgas circulated by said blower may pass; and (b) a cavity beneath saidtop portion defined by said shelf through which gas circulated by saidblower may pass; at least one air return path in each said cavity influid communication with said blower for return of said temperaturecontrolled gas to said blower; and a microwave source and wave guidethrough which microwaves travel, said wave guide having a plurality ofopenings through which said microwaves can pass into said cavity,wherein said microwaves traveling in said wave guide have a wavelengthand predetermined minima and maxima, said openings in said wave guidebeing positioned to substantially correspond with said minima or maxima.15. The thermal treatment apparatus of claim 14 wherein said openingsare in the form of louvers protruding from said top surface forsupporting a food receptacle.